expand()

[Stefan Weinzierl]

> You have to use color_ONE() instead of just "1" where appropriate (terms
> of a sum must all be of the same type):
>    ex g = (color_ONE()+eps*color_T(a)+pow(eps,2)*color_T(b))
>         * (color_ONE()-eps*color_T(c)+pow(eps,2)*color_T(d));
> This will produce the right expression on expand().

Hi Christian,

thanks for your reply. This is certainly a workaround, but I'm not too
comfortable with it.
My original problem occured in a user-defined algebra, I took the colour
matrices only as an example.

The question is what "expand()" should return for an expression like

 ( 1 + A ) * B

where A and B are in some algebra.
You say, that all terms of a sum must be of the same type, so that would
involve to define a unit element in the algebra called for example "ONE"
and write

 ( ONE + A ) * B

instead. This works.
But in this case I would think it's better if

 ( 1 + A ) * B

throws an exception instead of just returning A*B. Otherwise you introduce
a possible source of errors which is hard to track in complex programs.

 Stefan